Patients with atopic dermatitis (AD) have superficial skin colonization with Staphylococcus aureus and an increased number of T helper (Th)2 cells in their peripheral blood. The purpose of this study was to clarify the involvement of interleukin (IL)-10 secretion from Langerhans cells (LCs) in staphylococcal peptidoglycan (PEG)-induced Th2 immune responses in mice. Mice were primed with LCs pulsed with PEG (or LPS) and ovalbumin (OVA) and then given a booster OVA injection 2 days later in the hind footpad. Five days after the OVA injection, cytokine responses in the draining popliteal lymph nodes were investigated by RT-PCR and ELISA. Production of both IL-10 and IL-12 by cultured LCs was detected by ELISA. Administration of PEG- or LPS-stimulated LCs into the hind footpads of the mice induced Th2-prone and Th1-prone immune responses, respectively, as represented by expression of IL-4 and interferon-γ. In vitro experiments showed that PEG induced greater production of IL-12 p40 from LCs than did LPS, whereas LPS induced greater production of IL-12 p70 from LCs than did PEG. Furthermore, it was found that PEG-stimulated LCs induced greater production of IL-10 than did LPS-stimulated LCs, and that neutralization of IL-10 augmented IL-12 p70 production and inhibited Th2 development by PEG-stimulated LCs. These results suggest that PEG can induce Th2 development through down-regulation of IL-12 p70 production by LCs in an IL-10 production-dependent manner and would explain the role of S. aureus colonization in patients with AD.